Greetings Friend, interesting your application to load a battery, to know if the alternator is in good condition measures with a tester or polyimetter the battery voltage before pedaling (it should be around 12V) and then during the pedaling (above 13V, no more than 14.5V). The tightening of the pedaling is indicated that the alternator is working, those pulls are normal because internally the alternator generates "alternating current" of there is that the diodery enters into action and then the regulator. I don't know if it is viable suddenly to place a kind of flying style counterweight on the alternator pulley that helps with inertia to overcome those pulls. Good luck and keep telling us how the project is going. Greetings.